1. Field of the Invention
The present invention relates to an electric rotating machine, and particularly to an electric rotating machine using an oil with which deterioration in insulation performance due to discharge can be reduced.
2. Description of the Background Art
Japanese Patent Laying-Open No. 8-261152 discloses an electrically-driven compressor of hermetically-sealed type. This electrically-driven sealed-type compressor includes a sealed vessel, a stator, a rotor, a crankshaft, and a lubricating oil. The lubricating oil is stored in a bottom part of the sealed vessel. One end of the crankshaft is immersed in the lubricating oil.
The rotor is fixed to the crankshaft. The stator is provided around the periphery of the rotor. The stator includes a coil, and one of the two coil-ends of the coil is in contact with the lubricating oil.
The crankshaft has a hollow structure. A pump member for raising the lubricating oil is contained in the hollow inner part of the end of the crankshaft that is immersed in the lubricating oil. The pump member thus raises the lubricating oil by rotations of the crankshaft. The lubricating oil raised by the pump member is lifted through the crankshaft by centrifugal force generated by the rotations.
The lifted lubricating oil is applied, in the form of drops, through a hole in the other end of the crankshaft to cool a coil end of the stator for example and returned to the bottom part of the sealed vessel.
With the electrically-driven sealed-type compressor, as discussed above, the lubricating oil stored in the bottom part of the sealed vessel is circulated to cool the coil end for example.
When the lubricating oil is used for cooling the coil end, however, a difference in dielectric constant between an insulating material covering the coil and the lubricating oil causes intermittent changes in electric-field intensity, resulting in discharge on the interface therebetween to possibly cause damage to the insulating material.